1. Field of the Invention
The present invention is directed generally to wireless communication systems and, more specifically, to the transmission of control information to one from multiple reception points.
2. Description of the Art
A communication system includes a DownLink (DL) that conveys signals from one or more Transmission Points (TPs) to User Equipments (UEs) and an UpLink (UL) that conveys signals from UEs to one or more Reception Points (RPs). A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A TP or a RP is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), a NodeB, an access point, etc.
DL data information is conveyed through a Physical DL Shared CHannel (PDSCH). DL Control Information (DCI) for scheduling a PDSCH or a PUSCH transmission is conveyed through a respective DCI format transmitted in a Physical DL Control CHannel (PDCCH).
UL data information is conveyed through a Physical UL Shared CHannel (PUSCH). UL Control Information (UCI) is conveyed through a Physical UL Control CHannel (PUCCH) unless a UE transmits a PUSCH in which case at least some UCI can be included in the PUSCH. A UE may also simultaneously transmit data information in a PUSCH and UCI in a PUCCH.
UCI includes ACKnowledgment information, associated with a Hybrid Automatic Repeat reQuest (HARQ) process (HARQ-ACK), a UE transmits in response to receiving data Transport Blocks (TBs), Channel State Information (CSI) which informs a NodeB of a DL channel medium a UE experiences, and Rank Indicator (RI) information associated with spatial multiplexing of PDSCH transmissions to the UE. An UL RS can be used for demodulation of data or control signals, in which case it is referred to as DMRS, or for sounding an UL channel medium to provide UL CSI to a set of RPs, in which case it is referred to as Sounding RS (SRS).
FIG. 1 illustrates a PUSCH transmission over a Transmission Time Interval (TTI) according to the related art.
Referring to FIG. 1, a TTI consists of one subframe 110 which includes two slots. Each slot 120 includes NsymbUL symbols 130. Some symbols in each slot are used to a transmit DMRS 140. The transmission BandWidth (BW) includes frequency resource units referred to as Resource Blocks (RBs). Each RB includes NscRB sub-carriers, or Resource Elements (REs), and a UE is allocated MPUSCH RBs 150 for a total of MscPUSCH=MPUSCH·NscRB REs for a PUSCH transmission BW. A unit of one RB over one TTI is referred to as a Physical Resource Block (PRB). The last subframe symbol may be used to transmit SRS 160 from one or more UEs. The number of subframe symbols for data/UCI/DMRS transmission is NsymbPUSCH=2·(NsymbUL−1)−NSRS where NSRS=1 if the last subframe symbol is used to transmit SRS and NSRS=0 otherwise.
FIG. 2 illustrates a transmitter block diagram for data information and UCI in a PUSCH according to the related art.
Referring to FIG. 2, coded CSI symbols 205 and coded data symbols 210 are multiplexed by multiplexer 220. Coded HARQ-ACK symbols are then inserted by multiplexer 230 by puncturing data symbols and/or CSI symbols. A transmission of coded RI symbols is similar to the one for coded HARQ-ACK symbols (not shown). The Discrete Fourier Transform (DFT) is obtained by DFT unit 240, the REs 250 corresponding to a PUSCH transmission BW are selected by selector 255, the Inverse Fast Fourier Transform (IFFT) is performed by IFFT unit 260, the output is filtered and by filter 270, the signal is applied a certain power by Power Amplifier (PA) 280 and it is then transmitted 290. For brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas as well as encoders and modulators for the data symbols and the UCI symbols are omitted for brevity.
FIG. 3 illustrates a receiver block diagram for data information and UCI in a PUSCH according to the related art.
Referring to FIG. 3, after an antenna receives the analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not shown for brevity, the digital signal 310 is filtered by filter 320, a Fast Fourier Transform (FFT) is applied by FFT unit 330, a selector unit 340 selects the REs 350 used by the transmitter, an Inverse DFT (IDFT) unit applies an IDFT 360, a de-multiplexer 370 extracts the coded HARQ-ACK symbols and places erasures in the corresponding REs for data symbols and CSI symbols and finally another de-multiplexer 380 separates coded data symbols 390 and coded CSI symbols 395. A reception of coded RI symbols is similar to the one for coded HARQ-ACK symbols (not shown). Additional receiver circuitry such as a channel estimator, demodulators and decoders for data symbols and UCI symbols are not shown for brevity.
Assuming for simplicity a transmission of one data TB in a PUSCH, a UE determines a number of coded modulation symbols per layer Q′ for HARQ-ACK as in Equation (1)
                              Q          ′                =                  min          (                                    ⌈                                                O                  ·                                      M                    sc                                          PUSCH                      -                      initial                                                        ·                                      N                    symb                                          PUSCH                      -                      initial                                                        ·                                      β                    offset                    PUSCH                                                                                        ∑                                          r                      =                      0                                                              C                      -                      1                                                        ⁢                                      K                    r                                                              ⌉                        ,                          4              ·                              M                sc                PUSCH                                              )                                    (                  Eq          .                                          ⁢          1                )            
In Equation 1, ┌ ┐ is the ceiling function rounding a number to its next integer, O is a number of HARQ-ACK information bits, MscPUSCH is a PUSCH transmission BW in the current subframe for the data TB, NsymbPUSCH-initial is the number of subframe symbols for initial PUSCH transmission for the same data TB, βoffsetPUSCH=βoffsetHARQ-ACK is a value signaled to the UE from a TP by higher layer signaling, MscPUSCH-initial is a PUSCH transmission BW for initial PUSCH transmission for the same data TB, C is a number of code blocks, and Kr is a number of bits for code block number r. When a PUSCH contains only CSI, in addition to HARQ-ACK, the UE determines a number of coded modulation symbols per layer Q′ for HARQ-ACK as Q′=min(┌O·MscPUSCH·NsymbPUSCH·βoffsetHARQ-ACK/OCSI-MIN┐, 4·MscPUSCH), where OCSI-MIN is a minimum number of CSI information bits including Cyclic Redundancy Check (CRC) bits. A same determination for a number of coded modulation symbols per layer Q′ applies for a transmission of RI with βoffsetPUSCH replaced by βoffsetRI. For CSI, a number of coded modulation symbols per layer is determined as Q′ as
      Q    ′    =      min    (                  ⌈                              (                          O              +              L                        )                    ·                      M            sc                          PUSCH              -              initial                                ·                      N            symb                          PUSCH              -              initial                                ·                                    β              offset              CSI                        /                                          ∑                                  r                  =                  0                                                  C                  -                  1                                            ⁢                              K                r                                                    ⌉            ,                                    M            sc            PUSCH                    ·                      N            symb            PUSCH                          -                              Q            RI                                Q            m                                )  where O is a number of CSI bits, L is a number of CRC bits given by
  L  =      {                                        0                                              O              ≤              11                                                            8                                otherwise                              ,      and Qm is the number of information bits per modulation symbol. If RI is not transmitted then QRI(x)=0. The encoding process for the HARQ-ACK bits or RI bits or CSI bits is not discussed as it is not material to the objects of the present invention.
A transmission of an UL RS (DMRS or SRS) is through a Zadoff-Chu (ZC) sequence. UCI signals can also be transmitted in a PUCCH using a ZC sequence. Similar to a PUSCH transmission structure, a PUCCH transmission structure consists of one subframe which includes two slots and each slot also includes NsymbUL symbols. The exact partitioning of a PUCCH slot for transmissions of RS or UCI signals is not material to embodiments of the present invention and a respective description is omitted for brevity. A ZC sequence used to transmit an UL RS or a UCI signal can be generated directly in the frequency domain and a DFT is then be bypassed.
Improving coverage and cell-edge throughput are key objectives in a communication system. Coordinated Multi-Point (CoMP) transmission/reception and Carrier Aggregation (CA) are important techniques in achieving these objectives. CoMP enables a UE in a cell-edge region to reliably receive signals from a first set of NodeBs (DL CoMP) or reliably transmit signals to a second set NodeBs (UL CoMP). A set of NodeBs for DL CoMP or DL CA is referred to as a set of TPs while a set of NodeBs for UL CoMP or UL CA is referred to as a set of RPs. CA operation also enables a UE to communicate with different TPs or RPs, either in a same TTI or in different TTIs, which enables interference co-ordination, improved spectral efficiency, or high data rates for a UE connected to a pico cell while maintaining a coverage link with a macro cell.
FIG. 4 illustrates an UL CoMP operation according to the related art.
Referring to FIG. 4, a network includes a macro-NodeB 410 having a first DL coverage area 415 and a pico-NodeB 420 having a second DL coverage area 425. A macro-NodeB transmits with substantially larger power than a pico-NodeB and has a much larger DL coverage area. UE1 430 communicates in both DL and UL 435 with a macro-NodeB which provides both a single TP and a single RP for UE1. UE2 440 communicates in both DL and UL 445 with a pico-NodeB which provides both a single TP and a single RP for UE2. As a macro-NodeB transmits with larger power, it is a TP for UE3 450. However, in the UL, it is generally beneficial for a UE to communicate with a RP for which it experiences a smallest path-loss or a smallest interference. For UEs located at a similar distance to a macro-NodeB and a pico-NodeB, the RP can be either or both of these two nodes. For nodes that are not co-located, it is generally simpler to operate with a single RP. For UE3, this RP can be a macro-NodeB 454 or a pico-NodeB 456. The RP can change on a subframe basis considering cell loading or interference experienced by each node. This selection is referred to as Dynamic Point Selection (DPS).
Although FIG. 4 considers a pico-NodeB having a different cell identity than a macro-NodeB, a respective network operation is same if instead of a pico-NodeB a Remote Radio Head (RRH) having a same cell identity as a macro-NodeB is used. Then, in order to differentiate between a macro-NodeB and a RRH, a virtual cell identity may be assigned to an RRH to practically provide same functionalities as a physical cell identity for a pico-NodeB.
A key issue for CoMP operation or inter-NodeB CA operation is the connection speed between different NodeBs. Typical cable connections incur large data transfer delays and this requires that all delay sensitive control information be transmitted from or received at the NodeB performing the scheduling. Conversely, fiber optic links incur very small delays compared to the subframe duration, especially over short distances, and allow control information to be transmitted from or received at a NodeB other than the NodeB performing the scheduling as it can be quickly transferred from or to the latter NodeB. CoMP operation resembles CA operation with inter-NodeB scheduling. With CA, PUSCH or SRS transmissions on each cell have individual respective parameters including for power control and for ZC sequences.
For UL CoMP or inter-NodeB UL CA, different cells served by different NodeBs/RPs may operate with different BLER targets for data TBs according to the path-loss, UE loading, and interference conditions experienced by respective UEs. For intra-NodeB UL CA, different cells simply serve as data pipes in order to increase data rates and typically target a same BLER for data TBs from a UE as they intend to provide equivalent quality of service.
One consequence of the above operational differences between UL CoMP or inter-NodeB UL CA and intra-NodeB UL CA is that, as the UCI BLER is linked to the BLER of data TBs in a PUSCH, the UCI BLER in case of intra-NodeB UL CA is typically the same regardless of the PUSCH conveying the UCI but this may not apply in case of DPS UL CoMP or inter-NodeB UL CA. It is important to ensure the UCI BLER targets as, unlike data TBs, UCI does not benefit from HARQ retransmissions and has fixed BLER targets.
Another consequence is that for different locations of RPs, UCI may not be timely processed at the RP where the scheduler is located if UCI is included with data information in a PUSCH intended for another RP. As UCI is more delay sensitive than data information, it is beneficial to decouple the RP of UCI from the RP of data information especially for UL CoMP or inter-Node N UL CA operation over a slow backhaul link.
Therefore, there is a need to ensure UCI BLER targets for UL CoMP operation or for inter-NodeB UL CA operation.
There is another need to adjust a number of coded modulation symbols of a UCI type according to an intended RP.
Finally, there is another need to decouple UCI transmission from data information transmission for UL CoMP or for inter-NodeB UL CA.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.